This study has two long-term goals. The first is to determine the physiological role of phospholipid transfer proteins in regulating the structure and function of biological membranes. The second is to determine whether an altered lipid composition, perhaps as regulated by lipid transfer proteins, is a fundamental lesion underlying a number of anomalies of function that are known to be associated with neoplastic cell membranes. Three Morris hepatomas of various degrees of differentiation were examined. In all three, the levels of nonspecific lipid transfer protein (NS-TP) were reduced to 10% normal. All three tumors showed increased mitochondrial cholesterol content and decreased microsomal phospholipid content which correlated with growth rate, although only minor changes in phospholipid composition were observed. These results do not support previous hypotheses concerning the involvement of NS-TP in lipid transfer from the endoplasmic reticulum to other intracellular membranes or their "rate-limiting" involvement in cholesterol synthesis. In order to determine whether significant alterations were also apparent in plasma lipid, blood was taken from control and hepatoma-bearing rats. Though the phospholipid, cholesterol ester, cholesterol, and triglyceride distributions were found to be similar, elevated lipid content was observed in plasma samples of hepatoma-bearing rats, particularly for triglyceride and free cholesterol. Furthermore, a shift was observed in the lipoprotein pattern with more of the total lipid of hepatoma bearing rats found in the VLDL fraction and less in the HDL fraction. Studies have also been extended to hepatoma cells in culture (HTC). Increased cholesterol to phospholipid ratios were observed for mitochondrial and microsomal membranes of these cells compared to hepatocytes. Furthermore, low levels of NS-TP were found in cells grown in low-serum-containing media. Experiments are currently in progress examining the effect of elevated cholesterol levels on phospholipid biosynthetic activities and on the relationship of NS-TP to these activities and to lipoprotein secretion. (A)